In our country, cancers are the first of death causes among various diseases. Further, recent statistics show that the number of deaths from cancers is yearly increasing. There are a variety of views about its cause, but it has been desired to establish at once a new method for the treatment of cancers.
A variety of methods for the treatment of cancers have hitherto been attempted, including surgical operation, radiotherapy and chemotherapy, alone or in combination. In particular, surgical operation is highly effective in the removal of primary cancers, but it is inoperative for inoperable organ cancers and cancers in which a tumor metastasis is initiating. Radiotherapy and chemotherapy are often applied to inoperable primary cancers in organs or metastatic cancers. However, they have a tendency to injure a normal cell, which results in appearance of undesirable side effects such as reduction of immunological, metabolic and hematogenous functions, thus the scope of the application being limited. Even if growth of cancers in the specific region of the body is successfully inhibited by such radiotherapy or chemotherapy, growth of metastatic cancers in other regions may often lead to death of the patient.
Many reports state that the racemate, 2,3-dihydropolyprenol compounds have low side effects to an organism with the activities for suppressing the growth and metastasis of cancers (Japanese Patent Kokoku Hei 4-52251, Japanese Patent Kokai Hei 2-11513, Japanese Patent Kokai Hei 2-25415, Cancer Letters, 1991, vol. 57, 159-163). However, those compounds are not satisfactory for therapeutic agents for cancers.
Under such circumstances, there is a continuing desire to develop compounds having lower side effects to an organism and more potent inhibitory activities against the growth or metastasis of cancers than prior compounds.